Purpose :
To determine if change in lamina cribrosa depth occurs more frequently than change in neuroretinal parameters in glaucoma. Additionally, to determine whether Bruch’s membrane or anterior sclera should be used as reference plane when measuring laminar depth.

Methods :
In a prospective observational study, anterior laminar depth from a reference plane based on Bruch’s membrane (LD-BM) and anterior sclera (LD-AS) was measured with optical coherence tomography (Fig. 1). Two neuroretinal parameters, minimum rim width (MRW) and retinal nerve fibre layer thickness (RNFLT), in addition to peripapillary choroidal thickness were measured. Factors related to LD-BM and LD-AS were determined with mixed effects modeling. Cut-offs for significant change in each parameter were estimated from the variability in 35 healthy controls over a 1-year period. The occurrence of significant change in laminar depth and neuroretinal parameters were compared with survival models. Since normal aging has a clear effect on neuroretinal parameters but not on laminar depth, changes in neuroretinal parameters were adjusted for age-related reduction.

Results :
There were 155 glaucoma patients followed for a mean (range) of 3.90 (2.03 – 5.44) years. LD-BM was influenced significantly more by choroidal thickness (1.14 µm/µm, 95%CI: 1.07 – 1.21) than was LD-AS (0.15 µm/µm, 95%CI: 0.08 – 0.22). Posterior movement of the lamina (LD-BM increase or LD-AS increase) occurred with the same frequency as thinning in neuroretinal parameters (MRW decrease or RNFLT decrease; Fig. 2A). Anterior movement of the lamina was detected more frequently with the Bruch’s membrane (LD-BM decrease) compared to the anterior sclera (LD-AS decrease) reference plane (hazard ratio: 3.23, P < 0.01; Fig. 2B). Significant choroidal thinning occurred in the majority (25 of 28, 89%) of patients in whom anterior movement of the lamina occurred with the Bruch’s membrane, but not anterior scleral, reference plane (LD-BM decrease without LD-AS decrease). Patients had a wide range of individual rates of change of choroidal thickness, from -20.00 to 17.09 µm/y (mean -1.62 µm/y).

Conclusions :
Lamina cribrosa depth should be measured from an anterior sclera reference plane to reduce the influence of choroidal thickness changes. In glaucoma patients, changes in lamina cribrosa depth are detected with similar frequency as changes in neuroretinal parameters.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.